The main causes of left back pain include the following: 1, peptic ulcer, which is mainly due to poor dietary habits, destruction of the protective barrier of the gastric mucosa, as well as the infection of Helicobacter pylori leading to the breakage of the gastric mucosa and duodenal mucosa, and the formation of ulcers. The main manifestation is pain in the upper middle abdomen, and the pain can radiate to the left back, resulting in left posterior back pain. 2, cardiovascular disease, mainly seen in coronary atherosclerotic heart disease resulting in angina pectoris, acute myocardial infarction, etc., due to hypoxia and ischemia of cardiac muscle cells leading to symptoms in the precordial area, and can radiate pain to the left shoulder back. 3, intercostal neuralgia, mainly due to various causes of Intercostal nerve injury, as well as sterile inflammation of the intercostal nerve, etc., resulting in intercostal nerve pain, and when the posterior back intercostal nerve is involved there will be left posterior back pins and needles-like pain. 4. myofasciitis, muscle fasciitis caused by long time posture incorrectness.